... by splitting it into separate probe functions for the color and depth
buffer (hiz_probe_color_buffer() and hiz_probe_depth_buffer()).  By
separating the probe functions, we can write tests that focus on just one
feature.

Also, make the probe functions more general by adding a function parameter
that specifies the expected probe values.

Signed-off-by: Chad Versace <chad.versace@intel.com>